On the firewall mark the locations of the screw mounting holes of your engine mount. The centerline of your crankshaft should be around 1 to 1.25 inch down from the top of the firewall. Drill the holes first with a small drill bit. The holes in the following photo are 3/32″, but 1/16″ is preferable.
After the small pilot holes are drilled, enlarge the holes to 5/32″.
There’s a good reason for drilling small pilot holes first. A twist drill likes to wander, and the potential inaccuracy is related to the diameter of the bit. A smaller bit has a smaller potential inaccuracy. When you drill into an existing pilot hole the drill does not wander. So if you start small your holes will be a lot more accurate.
Place the 4-40 blind nuts into the holes from the inside, then thread the screws through the engine mount into the nuts, but don’t draw them tight yet.
Apply medium CA glue to the wood where the flange of the nut will make contact when it is drawn tight. The nut should be started in the hole before the glue is applied. This will help prevent the glue from entering the hole and contaminating the threads.
Don’t glue all the nuts at once, then tighten them all. Leaving glue around an untightened nut will increase the chance of thread contamination. Glue one nut and tighten it, then glue the next nut and tighten it, and so on. Once the nuts are all drawn tight, spritz a little bit of accelerator on them to keep you from gluing your finger into the airplane later.
Stand the airplane up on its tail and look at the throttle arm. Use your line of sight to mark the throttle cable location with a pen.
Drill the hole with a 1/8″ bit. Lean the drill about 5 to 10 degrees to enlarge the hole just a little bit, wobbling the drill around in a circle. This will help you stuff the cable housing in. If you leave the hole exactly 1/8″ it will be pretty tight.
Roughen about 1/2″ of the cable housing tube with sand paper on one end. Install the housing in the holes in the firewall and F2, with the roughened end at the firewall. Let it protrude out of the firewall about 1/8 to 1/4 inch to help you avoid getting glue inside the tube. Glue the tube in place with CA.
When the glue has cured, trim the excess length and sand it flush.
Use medium CA to attach 1/8″ plywood F5 to the top of the firewall and the fuselage sides. Then use Medium CA to attach lite ply F6 to the underside of F5. Push it all the way to the firewall before sticking it in place.
Stick F7 to the underside of the hatch. The grain of the hatch is crosswise to the fuselage, and F7 should go at the rear edge. F7 is an inch wide, and it should be attached so half an inch is glued to the hatch and half an inch protrudes. Place it so the hatch will be centered on top of the fuselage when it’s set in place with F7 in between the fuselage sides.
Put the hatch in place and make a mark on both sides of the fuselage to show how far back the hatch will extend.
Cut a piece of 1/8″ balsa sheet about an inch wide, and about 3.5″ long. The idea is to make it just a little bit wider than the fuselage.
Push it back against the struts and mark the inside dimension between the struts on the balsa with a hobby knife, using the struts as a guide. Measure from the back edge of the hatch to the struts and mark this distance on your piece.
Cut out the balsa to allow it to fit between the struts. Don’t forget to slant your cut.
Put the piece in place and trim it if necessary to make it fit nicely. Don’t forget the hatch is supposed to fit in place at the same time.
When it fits correctly, lay another piece of 1/8″ balsa sheet across the top, behind the struts, to give you a guide for the piece you just cut. The tops should be flush.
When you get it right, glue the piece in place with CA. (Remove the hatch to keep from gluing it in place.) It may also be helpful to turn the fuselage over and glue your balsa piece from the bottom.
Cut another piece of 1/8″ sheet and use a hobby knife to mark the space between the rear spars. Sorry about the blurry photo. That’s a hobby knife marking the inside edge of the strut.
Cut out each side to accommodate the struts. Don’t forget to slant the edges that meet the front of the struts.
The rear edge of the sheet should protrude past the rear struts.
Glue this piece in place with CA. The part that protrudes behind the struts should be trimmed and sanded flush with the rear edge of the struts.
Cut another piece of 1/8″ sheet to form the instrument panel. Bevel the bottom edge. Attach it to the rear edge of the struts and the rear edge of the top sheet with CA glue.
Cut another piece of 1/8″ balsa to fill the space between the two sheets you just installed, completing the decking on top of the fuselage.
Use a utility knife and a sanding block to make the bottom of F2 flush with the bottom of the fuselage. Remove any glue blobs from around the tabs on the fuselage.
Trim the notches of both layers of F4 (landing gear plate) if necessary to make them fit on the bottom of the fuselage. Do not glue the two layers together before attaching them to the fuselage. The reason why they are attached one layer at a time is because if you glue them together first they will probably be a little bit crooked. Adding them one at a time will make alignment a lot easier.
Put medium CA glue on the fuselage sides and F2 where F4 makes contact.
Attach one layer of F4 and press it with your hand until the CA glue sticks. Then add more medium CA on the outside of the first layer of F4. Make sure you put some glue around the alignment tabs so the gaps will be filled.
Add the second F4 layer and press by hand until the CA sets. Any remaining gaps around the tabs can be filled with medium CA and cured with accelerator.
Mark the landing gear for holes as shown in the diagram:
Drill the holes with a small bit, such as 3/32″.
Line up the front edge of the landing gear with the front edge of the landing gear plate F4 on the bottom of the fuselage.
Drill the holes through F4.
Drill the holes to the correct size. If you’re mounting the gear with 6-32 screws, drill the holes in the wood to 3/16″ for the blind nuts, and drill the holes in the aluminum 5/16″ for the screws. Install the blind nuts the same way you did the ones on the firewall for the engine mount.
Nylon bolts will allow the landing gear to shear off in the event of a crash. If you want to mount the gear with 1/4″ nylon bolts you will need to drill 1/4″ holes in the aluminum. Drill the holes in the wood with a #7 drill (.201″). 3/16″ will also work. Harden the holes with thin CA. Don’t put the tap in when the glue is still wet or it will gum up your tap. Wait a while for it to cure or shoot a little bit of accelerator if you don’t feel like waiting. Use a 1/4-20 tap to thread the holes. Trim your bolts to 1/2″ length.
Sand the bottom of the firewall to match the angle of the bottom of the fuselage. Attach the 1/4″ balsa chin blocks with CA.
Drill 1/4″ holes in the firewall for your fuel lines (or for motor wires). The holes in the photo are in the middle of a Dave Brown 40 size engine mount.
